Known microorganisms capable of producing isoamylases include yeast (see NOGEI KAGAKU KAISHI Vol. 23, pp. 115-120, pp. 120-123 (1949)), Cytophaga (see FEBS Lett., Vol. 12, pp. 96-100 (1970)), and Pseudomonas (see Biochem. Biophys. Acta, Vol. 212, pp. 458-469 (1970)).
These conventional isoamylases have several disadvantages in industrial use. Isoamylase of yeast origin has poor heat stability. Isoamylase of Cytophaga origin has insufficient heat stability and acid resistance. On the other hand, isoamylase of Pseudomonas origin, while such does not have the problem of heat stability and acid resistance, involves disadvantages in productivity, i.e., need of a long cultivation time and low activity attained. Thus, conventional isoamylases are unsatisfactory for use on an industrial scale.